Which is a nice-sounding idea until the OS components are growing stale, at which point you'll be wondering why, for instance, your scripting language of choice

Which is a nice-sounding idea until the OS components are growing stale, at which point you'll be wondering why, for instance, your scripting language of choice's hash libraries don't support the modern idea of SHA256 (the answer being: because the OpenSSL version shipped with OS X was too old), or why your builds are now failing (because Apple shipped a library update without updating the headers in a Software Update). Homebrew tries to take the high ground here, but it's just naivety. They'll wind up installing "duplicate" versions of software too -- in fact, they already are doing so. The short-cycle of Leopard -> Snow Leopard won't be happening again soon, and the only alternative to adding "duplicate" software to your dependency tree is letting software go stale (for example: python 2.7 vs SL's 2.6.1). It's easy to say that the 10 years of knowledge that both MacPorts and Fink have about the platform is "stupid" when you haven't had the experience of maintaining a working packaging/port system through a few OS X release cycles, and aren't familiar with the problem space or Apple's policies.